1. Field of the Invention
The present invention relates to liquid crystal display devices, and more particularly, to device and method for driving a liquid crystal display device: in which a level of a driving voltage is varied with variation of a temperature of an environment in which a liquid crystal display device is used for improving a quality of a picture displayed on the liquid crystal display device.
2. Discussion of the Related Art
In general, the liquid crystal display device controls a ratio of light transmission through liquid crystals by using an electric field for displaying a picture. To do this, the liquid crystal display device is provided with a liquid crystal display panel having a matrix of pixel regions, and a circuit for driving the liquid crystal display panel.
In general, the liquid crystal display device displays the picture by controlling the ratio of light transmission through the liquid crystals having dielectric anisotropy. To do this, the liquid crystal display device is provided with a liquid crystal display panel having a matrix of pixel regions, and a circuit for driving the liquid crystal display panel.
The liquid crystal display panel is provided with a plurality of gate lines and data lines arranged to cross each other, and the pixel regions at regions defined as the gate lines and data lines cross each other, respectively. The liquid crystal display panel is also provided with pixel electrodes and a common electrode for applying the electric field to the pixel regions. Each of the pixel electrodes is connected to a thin film transistor (TFT) which is a switching device. The TFT is turned on by a scan pulse from the gate line to charge a data signal from the data line to the pixel electrode.
The driving circuit is provided with a gate driver for driving the gate lines, a data driver for driving the data lines, a timing controller for supplying control signal for controlling the gate driver and the data driver, and a power source unit for supplying power to the liquid crystal display panel, the gate and data drivers, and the timing controller.
The gate driver has a shift register for forwarding the scan pulses in succession. The shift register has a plurality of stages connected in a cascade. Each of the plurality of stages has at least one of a plurality of the clock pulses having phase differences in succession applied thereto, and forwards the scan pulses in succession for scanning the gate lines in succession.
The liquid crystal display device has applications to various products, up to monitors, cellular phones, and personal terminals. According to this, because the liquid crystal display device can be used, not only within a fixed space, but also during in motion, and inside and outside of a building, it is required that the liquid crystal display device is designed to have resistance to an environmental temperature. For an example, permittivity of the liquid crystal filled in the liquid crystal display panel, resistance of the liquid crystal display panel itself, and the like vary sensitive to variation of the temperature. The variation of the permittivity of the liquid crystals and the resistances of the liquid crystal display panel can influence a driving range of the liquid crystals, and a change rate of a driving voltage level for driving the pixels in the liquid crystal display panel.
Because a waveform of a pixel voltage changes with reference to a common voltage if the level of the driving voltage applied to the pixels changes, even gradation of the picture displayed on a screen changes following change of a voltage difference between the pixel voltage and the common voltage. Therefore, since display of a picture of an accurate gradation is not possible, there has been a problem in that a quality of the picture becomes poor in overall, such as drop of a contrast ratio of the picture.